1. Field of the Invention
The invention relates to a headlight or lamp used in an automobile or other vehicle, and more particularly to a configuration of the headlight in which a single light source, such as a discharge lamp, is incorporated. The single light source headlight is capable of changing light distribution patterns between a by-passing mode when the automobile is passing another vehicle and a traveling mode when the automobile is traveling straight ahead. Light distribution patterns are changed by changing a position of a part in the headlight affecting formation of light distribution patterns, such as a light source or a reflector, in accordance with the driver's operations.
2. Discussion of the Related Art
FIG. 6 illustrates a conventional automobile headlight 90. The headlight 90 includes a light source 91, a reflector 94 having an aperture, a light source mounting plate 92 having a fixed end and a movable end, a solenoid 93 connected to the movable end portion and capable of moving the light source mounting plate 92 to traverse a circular arc with the center located at the fixed end, and a return spring 95 which is also connected to the movable end portion to return the light source mounting plate 92 to a previous position when the solenoid 93 is turned off. Light distribution patterns of the headlight 90 can be repeatedly switched between a by-passing mode and a traveling mode by changing the position of light source 91 relative to the reflector 94 in accordance with the movement of the light source mounting plate 92 driven by solenoid 93.
Solenoid 93 and the return spring 95 produce predetermined forces in opposite directions to each other in order to pull the light source mounting plate 92 toward themselves, respectively. Since in current traffic environments there are more situations which require a headlight to be in by-passing mode, the standard position of the light source 91 is in the by-passing mode. Solenoid 93 is activated only during the traveling mode. When the headlight is switched from the traveling mode to the by-passing mode, the solenoid 93 is turned off, and the light source mounting plate 92 returns to its standard, original position by force of the return spring 95.
FIG. 7 illustrates a construction of another conventional automobile headlight 90. The headlight 90 includes a light source 91, a reflector 94, a light source mounting plate 92, a nut 96 connected to the light source mounting plate 92, a bolt 98 which screws through the nut 96, and a motor 97 corresponding to a head of the bolt 98 and connected to the bolt 98. In this configuration, the light source supporting plate 92 is not required to have a fixed end acting as a center for partial rotation thereabout. A return spring 95 is also not required if the motor 97 is capable of repeatedly screwing in or out a predetermined portion of the bolt 98 through the nut 98.
The conventional automobile headlight 90 as shown in FIG. 6 has the following problems. First, when the light source mounting plate 92 is moved from its by-passing position to its traveling position, the solenoid 93 requires high power because the light source mounting plate 92 is driven against the fairly strong bias of the return spring 95. The return spring 95 must maintain the light source mounting plate 92 in its original position while surviving the shock and vibration caused by travel of the car. Accordingly, the return spring 95 must deliver a fairly strong pulling force toward the reflector 94 even when the light source 91 is in its original position. Second, the solenoid 93 must be relatively large in size to produce the continuous power supply necessary when the light source mounting plate 92 is in the traveling position. The continuous power supply can cause a rapid temperature rise in the solenoid 92 and requires the solenoid 92 to be sized to withstand such a temperature rise.
The automobile headlight 90 as shown in FIG. 7 enables reduction of size and power consumption as compared to the headlight 90 shown in FIG. 6 since the driving force of the motor 97 is transmitted to the bolt 98 and the nut 96 and because the motor 97 can be turned off after the light source mounting plate 92 reaches a desired position. The light source mounting plate 92 is not required to have a fixed end acting as a center for partial rotation thereabout. Additionally, if the motor 97 can perform reverse rotation, a return spring 95 is not required. However, the automobile headlight 90 still has at least the following problems. If the motor 97 malfunctions, the light source mounting plate 92 may become fixed and unmovable in a position at which the malfunction of the motor 97 occurred. Accordingly, the headlight 90 may operate in an incorrect mode and/or incorrectly operate in between the traveling and by-pass modes.